AMO Physics with Intense XUV and X-ray Free Electron Lasers John T Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University ¡ h#p://www.ncpst . ie ¡ h#p://www.physics.dcu.ie/ ~jtc ¡ AICQT, Maynooth 1 June 2016
DCU Laser Plasma-AMO Physics Group Laser Plasma/AMO Physics @ NCPST - 6 laboratory areas focussed on pulsed laser matter interactions (spectroscopy/ imaging / particle detection) Principal Investigators (6): John T. Costello, Eugene T. Kennedy (Emeritus), Lampros Nikolopoulos (T), Jean-Paul Mosnier & Paddy Hayden (SFI SIRG PI) Current Postdocs (2): Dr. Pramod Pandey & Dr. Mossy Kelly Current PhD students (9) : Nichola Walsh, Ben Delaney, Stephen Davitt, Hu Lu, Getasew Wubetu, William Hanks, Muhammed Alli, Sadaf Syedah & Lazaros Varvarezos Recent Int’l Interns (2012-16): K Nishant/R Tejaswi, (LNMIIT, Jaipur), C Hand, (NUIM), S Reddy/R Namboodiri/A Neettiyath (IIT Madras), R Singh/S Gupta (IIT Kanpur), S Howard (Notre Dame), I-M Carrasco Garcia (Malaga), R. Black (Notre Dame), P Colley (Notre Dame) Recent PhD Grads (2009-2016): Padraig Hough, Conor McLoughlin, Rick O’Haire, Vincent Richardson, Dave Smith, Tommy Walsh, Jack Connolly, Jiang Xi, Leanne Doughty, Eanna MacCarthy, Colm Fallon, Mossy Kelly, D Middleton, Cathal O’Broin, Brian Sheehy & Saikumar Inguva AICQT, Maynooth Recent Past Postdocs (2012-2015): Satheesh Krishnamurthy (Open Univ. UK), Pat Yeates 1 June 2016 (Elekta Oncology UK) & Subhash Singh (U. Allahabad), Colm Fallon (IC4 – DCUBS).
Collaboration @ FLASH-DESY & FERMI- ELETTRA XFEL: P. Radcliffe & M. Meyer Paris (UPMC): R. Taieb (T) & A. Maquet (T) FERMI: P. O’Keefe, L. Avaldi & K. Prince DESY (Hamburg): K. Tiedke, S. Düsterer, W. Li, A. Sorokin & P. Jurani ć ,J. Feldhaus Orsay: D. Cubaynes Queen ’ s University Belfast: C. L. S. Lewis Moscow State University : A. N. Grum-Grzhimailo, E. V. Gryzlova, S. I. Strakhova Crete: P. Lambropoulos (T) Oulu/GSI: S. Fritzsche (T) DCU: T. J. Kelly, N. Walsh, E. T. Kennedy, L Nikolopoulos & J. T. Costello AICQT, Maynooth 1 June 2016
Collaboration @ LCLS X-ray FEL (SLAC) DESY (CFEL): I. Grguras, M Hoffmann & A. Cavalieri DESY (FLASH): S. Düsterer & J. Feldhaus DCU: T. J. Kelly, E. Kennedy, V. Richardson, L. Nikolopoulos (T) & J. T. Costello MPQ/TU-Munich: A. Maier, W. Helml, W. Schweinberger & R. Kienberger Ohio (OSU): C. Roedig, G. Doumy* & L. DiMauro Tohuku University: K. Ueda Hiroshima University: S. Wada SLAC: R. Coffee, J. Hastings, C Boestedt, J. Bozek et al. XFEL Gmbh: P. Radcliffe, T. Tschenscher & M. Meyer Moscow State University: N. Kabachnik AICQT, Maynooth Thanks to Paul Emma et al. 1 June 2016
Some members of the LCLS collaboration AICQT, Maynooth 1 June 2016
TIMESCALES - HOW FAST IS FAST ? One Computer month Human existence Camera Age of flash clock cycle 10 fs light pulse pyramid Age of universe s 1 minute -14 10 -9 10 -4 10 1 6 11 10 16 10 10 10 Time (seconds) zs fs ps as 10 -15 s 10 -21 s 10 -18 s 10 -12 s
X-ray – How X-ray is X-ray ? Spectral Range: IR to the X-ray Graphic: Courtesy, Prof. David Attwood (Berkeley) AICQT, Maynooth 1 June 2016
What do we want in an X-ray laser ? The Holy Grail is an X-ray laser with variable pulse duration on the femtosecond to attosecond timescales with tunable wavelength, variable polarisation and high energy per pulse (few 100 µ J to few 10 mJ) … .. AICQT, Maynooth 1 June 2016
X-ray Free Electron Lasers (FEL) Main Components of an X-ray FEL AICQT, Maynooth 1 June 2016
SASE-FEL, Fundamental Principle λ U λ ph (c-v)t vt N u λ U = vt N u λ L = (c-v)t ⇒ λ L ~ λ U (c-v)/v ~ λ u /2 γ 2 λ L = λ u (1+K 2 /2)/2 γ 2 γ = E/mc 2 1GeV machine γ ~ 2000 K = eB λ u /2 π mc λ u ~ 2.7 cm / λ laser ~ 6nm Electron bunch slips behind the Wavelength tunable – lightwave by λ per undulator by electron beam energy or period by tuning the undulator gap AICQT, Maynooth 1 June 2016
FLASH X-ray Free Electron Lasers (FEL) Overview RF-gun Diagnostics Accelerating Structures Collimator Undulators Bunch Bunch Laser Compresso Compressor FEL 5 MeV 127 MeV 450 MeV 1000 MeV Bypass r Diagnostics 300 m • LINAC Energy : ~ 1 GeV ~ 4 – 60 nm FLASH - Operation & Physical Layout AICQT, Maynooth 1 June 2016
X-ray Free Electron Lasers (FEL) LCLS Overview and Specifications lcls.slac.stanford.edu AICQT, Maynooth 1 June 2016
X-ray Free Electron Lasers (FEL) XFEL – Under Construction …… 2017 AICQT, Maynooth 1 June 2016
X-ray Free Electron Lasers (FEL) XFEL – Under Construction …… 2017 AICQT, Maynooth 1 June 2016
USPs of XUV & X-ray FELs (XFELs)? • High flux per pulse – typ. 10 13 photons/pulse • Tunable pulsewidth – from 1 to few 100 fs • Ergo high peak intensity – up to few 10 20 W.cm -2 possible • Seeded and unseeded modes now possible • Unseeded bandwidth – 0.2 – 1.0% • Seeded bandwidth – 0.005% (typ.) / λ / Δλ Δλ ≥ 10 4 • Synchronisation to optical fs lasers relatively easy AICQT, Maynooth 1 June 2016 • EUV/EUV and X-ray/X-ray pump-probe possible
Technology Now … .. So the Holy Grail is now largely realised as the SASE EUV and X-ray FELs at SLAC-Stanford, SCSS & SACLA-RIKEN, FLASH-DESY (+future European XFEL), FERMI@ELETTRA- Trieste, SwissFEL-PSI, Pohang, Shanghai, Dalian, etc …… .. AICQT, Maynooth 1 June 2016 Very recently [2012] seeding of LCLS, SCSS and FERMI have resulted in
Ionization in Intense Fields 1. Rudiments of ionization processes in intense laser fields 2. Photoionization experimental setups (FLASH & DESY) 3. One colour – two photon ionization 4. Two colour Ionization – physics and characterisation 5. Some conclusions AICQT, Maynooth 1 June 2016
The Atomic Photoelectric Effect a) Single Photon Ionization (SPI) b) Multi Photon Ionization (MPI) KE(e - ) = h ν EUV - IP KE(e - ) = nh ν NIR - IP e - IP IP (EUV Synchrotron) (NIR Laser) AICQT, Maynooth 1 June 2016
What happens as the laser intensity (field strength) grows ? Intensity/ Wavelength Photon Energy AICQT, Maynooth 1 June 2016
How can you determine in which regime the interaction resides ? Keldysh Parameter IP γ = IP = Ionization Potential 2 U p Up = Ponderomotive Pot. 2 µ m ( ) λ U P = 9.3 × 10 − 14 I Wcm − 2 ( ) eV * L V Keldysh, Sov.Phys-JETP 20 1307 (1965) AICQT, Maynooth 1 June 2016
Keldysh - Ionization Regime Multiphoton Ionization Tunnel Ionization Field Ionization γ >>1 γ ~ 2 γ <<1 Example: Helium in intense laser fields For Ti-sapphire laser: 800 nm, 10 15 Wcm -2 , γ ~0.45 (TI/FI regime For an EUV laser: 8 nm, 10 15 Wcm -2 , γ ~45 (MPI regime) So for EUV lasers, multi-photon ionization is the primary processs and will involve few photons and potentially few electrons AICQT, Maynooth 1 June 2016
USPs of XUV & XFELs in AMO Physics ? • Ultra-dilute targets • Photo -processes with ultralow cross-sections • Pump and probe experiments (EUV + EUV or EUV + Opt.) • Single shot measurements • Few-photon single and multiple ionization processes NB1: Makes inner-shell electrons key actors in non- linear processes for the first time AICQT, Maynooth 1 June 2016 NB2: Re-asserts primacy of the photon over field
Experimental Setups (DESY & SLAC) 1. Rudiments of ionization processes in intense laser fields 2. Photoionization experimental setups (FLASH & LCLS) 3. One colour – two photon ionization 4. Two colour Ionization AICQT, Maynooth 1 June 2016 5. Some conclusions
Photoelectron Spectroscopy @ Two colour ATI/ Laser Assisted FLASH PES Experimental Layout at FLASH - (EU-RTD) AICQT, Maynooth 1 June 2016
AMO PES Chamber at LCLS Rendered Image: High Field Chamber (AR-ETOF) and Diagnostics (MBES) Chamber Focussing Optics K-B Mirrors http://lcls.slac.stanford.edu AICQT, Maynooth 1 June 2016
Two Photon Ionization (TPI) of Xe and Kr atoms in an Intense Field 1. Rudiments of ionization processes in intense laser fields 2. Photoionization experimental setups (FLASH & DESY) 3. One colour - two photon ionization 4. Two colour Ionization 5. Some conclusions AICQT, Maynooth 1 June 2016
Non-linear processes in the EUV & X-ray Question. What is the simplest experiment you can carry out in non-linear optics ? Answer. Either two-photon absorption (TPA) or second harmonic generation (SHG) …… .. 3 694 nm 420 nm 2 694 nm 1 AICQT, Maynooth 1 June 2016
Motivation - Xe TPI in intense EUV fields Sorokin, Richter et al., PTB, PRL 2007 – Ion Spectroscopy !! AICQT, Maynooth 1 June 2016
Xe + h ν (93 eV) - Xe + (4d -1 ) + e - (~25 eV) FEL only. h ν ~ 93 eV Xe + h ν → Xe n+ + e - Intensity scaling... Weakest field … Replace Ion TOF by MBES – photoelectron spectroscopy AICQT, Maynooth 1 June 2016
Xe + 2h ν (93 eV) - Xe + (4d -1 ) + e - (~ 118 eV) Now ramp up the intensity to > 10 15 W.cm -2 ………… . • Using MBES, first evidence of two photon inner shell ionisation, (in this case) of 4d electron – Xe + 2 hv → Xe + 4d 9 + e - • ‘Retardation field’ applied to suppress low KE electrons (one photon processes) – hence electrons detected are due solely to multiphoton events • Energetically – 2 × (93) eV – 118 eV = 68 eV Phys Rev Lett 105 013001 (2010) ¡ • Yield scales quadratically, n=1.95 ± .2
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